1. Field of the Invention
The present invention relates to a recording sheet on which a toner image is formed by electronic photography or electrostatic recording method.
The present invention further relates to an image forming apparatus such as an electronic photographic system, electrostatic recording system or the like, and more particularly, it relates to a method and an apparatus for forming an image, which has a detecting means for detecting a recording sheet on which a toner image is formed.
2. Related Background Art
In the past, the technique in which a monocolor toner image is formed on a recording sheet comprising a transparent film made of polyester by means of an electronic photographic system and the toner image is used in an OHP (overhead projector) as a projecting image has been practically utilized.
Recently, in such electronic photographic system, in order to detect a moving condition of the recording sheet in the system, a permeable-type optical sensor wherein the presence of the recording sheet is detected by interrupting a light beam from a light source such as an LED (by the recording sheet) to change an output signal from a photoelectric converting element such as a CCD, photo-coupler or the like, or a reflection-type optical sensor wherein the presence of the recording sheet is detected by changing an output signal from a photoelectric converting element whether a light beam from a light source is reflected by the recording sheet or not has been used, thereby reducing the cost of the system and ensuring the detection accuracy and/or stable movement of the recording sheet in the system.
If the transparent film such as a polyester film or the like is used as the recording sheet, since the light source such as the LED has a luminous wave length from visual light to infrared light, it is difficult to absorb or reflect the light from the LED, which results in the failure in the detection of the recording sheet. To avoid this, the technique in which an opaque portion for absorbing or reflecting the light from the LED is provided on a part of the transparent film has been proposed, as disclosed in the Japanese Patent Laid-Open Nos. 58-90647, 58-105157 and 59-7367.
Such opaque portion is obtained by painting on the transparent sheet the paint capable of cutting the light from the LED by 60% or more, or by adhering a paper or cloth strip on the transparent sheet, or by deposing on the transparent sheet a metal capable of shielding the infrared luminous LED, thereby permitting the detection of the sheet. As shown in FIGS. 2A to 2D, such opaque portion is formed on the transparent rectangular sheet along its one, two, three or four edges thereof with a constant width, as illustrated by a hatched area. Further, as disclosed in the Japanese Patent Laid-Open No. 58-106550, a plurality of opaque portions are formed on the transparent sheet as illustrated by hatched areas in FIGS. 2E to 2H, whereby, if the sheet is jammed in the system, the jammed portion of the sheet can be easily determined or ascertained.
On the other hand, in order to improve the adhesion feature of the toner to be fixed and/or to improve the permeability and color reappearance feature of the colored image, as a recording sheet such as a transparent sheet or the like used with a recording apparatus of the electronic photographic system, the Applicant has proposed a transparent sheet including front and back surfaces having different functional features by coating a transparent resin material (on which a color toner image is formed) on a transparent film.
In case of such recording sheet, it is necessary to determine the front surface and back surface of the recording sheet. However, the conventional recording sheet has no means for determining the front and back surfaces thereof, detected by the recording apparatus.
Further, in the conventional image forming apparatuses, if the recording sheet including the front and back surfaces having the different functional features is used to form the image thereon, when an operator handles the recording sheet with erroneous judgement of the front and back surfaces thereof, the image is formed on the surface on which the resin material is not coated, thus resulting in the poor image formation.
In order to eliminate such drawback, although it can be considered that the both surfaces of the film (recording sheet) are coated by the resin material, there will arise a problem that the recording sheet as consumption goods becomes expensive and the primary function of the recording sheet cannot be carried out.